docker_run fails if selinux enabled

[safforddr]

On systems with selinux enabled (such as Fedora), the bind mount of /workspace fails.
This is easily fixed with the ":Z" option on the bind mount, which labels the mount properly.
Specifically in docker_run changing the last line
docker run -v "$(pwd):/workspace" -w /workspace "${docker_image}" "$@"
to
docker run -v "$(pwd):/workspace:Z" -w /workspace "${docker_image}" "$@"
makes the invocation work fine on Fedora.

This should not break other systems, but I only tested on Fedora.